package com.interviews.readwritelock;


import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * 读写锁示例
 *
 * @author qian
 * @version 1.0
 * @date 2022/2/22 14:13
 */
class Mycache {

    private volatile Map<String, String> map = new HashMap<>();

    private final ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();


    public void put(String key, String value) {
        rwLock.writeLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + "\t 正在写入：" + key);
            // 暂停一会线程
            try {
                TimeUnit.MILLISECONDS.sleep(300);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            map.put(key, value);
            System.out.println(Thread.currentThread().getName() + "\t 写入完成");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            rwLock.writeLock().unlock();
        }
    }

    public void get(String key) {
        rwLock.readLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + "\t 正在读取");
            try {
                // 暂停毫秒
                TimeUnit.MILLISECONDS.sleep(300);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            String value = map.get(key);
            System.out.println(Thread.currentThread().getName() + "\t 读取完成:" + value);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            rwLock.readLock().unlock();
        }
    }


}

/**
 * 多线程同时读一个资源类没有问题，所以为了满足并发量，读取资源应该可以同时进行
 * 但是
 * 如果有一个线程想去写共享资源，就不应该在有其他线程对该资源进行读或写
 * 小总结： 读读共存
 *        读写不能共存
 *        写写不能共存
 * 写操作：原子+独占
 */
public class ReadWriteLockDemo{
    public static void main(String[] args) {
        Mycache readWriteLockDemo = new Mycache();

        for (int i = 0; i < 5; i++) {
            final int i1 = i;
            new Thread(() -> readWriteLockDemo.put(i1 + "", i1 + ""), String.valueOf(i)).start();
        }


        for (int i = 0; i < 5; i++) {
            final int i1 = i;
            new Thread(() -> readWriteLockDemo.get(i1 + ""), String.valueOf(i)).start();
        }

    }
}
